1. Field of the Invention
This invention relates to a tilting and telescope traveling steering column arrangement for use in a motor vehicle such as an automotive vehicle, and more particularly to improvements in telescope traveling and tilt mechanisms of the steering column arrangement.
2. Description of the Prior Art
A variety of tilting and telescope traveling steering column arrangements have been proposed and put into practical use in the field of automotive vehicles. In such a tilting and telescope traveling steering column arrangement, the telescope traveling mechanism is usually arranged as follows: A part of a steering shaft on which a steering wheel is mounted is axially slidably fitted in a fixed tube fastened to a movable bracket, in which the splines of the part of the steering shaft are in engagement with the splines of the fixed tube. This allows the steering shaft to axially move relative to the fixed tube. The steering shaft is coaxially fitted with a telescopic upper jacket which is coaxially fitted in a telescopic lower jacket fixed to the movable bracket. The telescopic upper jacket is formed with a threaded portion which is engaged with a threaded portion of a telescopic sleeve. The telescopic sleeve is rotated around its axis by an electric motor, thus axially displacing the steering shaft. The above-discussed telescope traveling mechanism is disclosed, for example, in Japanese Patent Provisional Publication Nos. 60-4464 and 60-18449.
However, extension and contraction motions of the steering shaft are accomplished under engagement of external and internal threads, in which the external and internal threads displace axially relatives to each other upon rotation. Since such engagement of the external and internal threads are considerably high in frictional resistance, a relatively large force is required to axially displace the steering shaft. Accordingly, the electric motor is required to have a high output capacity and therefore becomes high in cost. As a result, an electrically operated telescope traveling mechanism can be used only in high grade automotive vehicles. Additionally, such a high output capacity electric motor is usually large-sized, and therefore a larger passenger compartment space is required to avoid contact of the passenger's knee with the electric motor in case the electric motor is installed the steering column arrangement. This provides inconvenience in design of automotive vehicle.
The tilt mechanism of the tilting and telescope traveling mechanism is usually arranged as follows: The steering shaft on which the steering wheel is mounted is fixed to the movable bracket which is rotatably supported through a tilt hinge to the fixed bracket. Accordingly, the steering wheel can set at a desired height position by rotating the movable bracket relative to the fixed bracket. More specifically, a tilt screw is provided between the movable and fixed brackets. A nut which is axially fixed to the fixed bracket is engagingly mounted on the tilt screw and axially rotatable by an electric motor to axially displace the tilt screw so as to push up the movable bracket. This causes the steering shaft to tilt upwardly.
However, axial displacement of the tilt screw relative to the nut is accomplished under engagement of external and internal threads, and therefore a clearance is unavoidably formed between the external and internal threads. This clearance unavoidably produces a so-called play between the movable and fixed brackets, thereby rendering the steering wheel unstable. Accordingly, the steering column arrangement produces vibration and vibration noise particularly during high speed cruising, thus disturbing comfortable driving.